The invention relates generally to humidifiers, and, in particular, to humidifiers used in conjunction with a medical gas delivery device such as a ventilator.
Hospitals commonly provide a supply of breathable gas from an artificial respirator or ventilator to patients for various medical reasons. It is preferable to control both the relative humidity and the temperature of the gas being delivered to the patient. More particularly, humidification requirements typically consist of between 28 and 31 mg/H.sub.2 O/L gas at 37.degree. C. which minimizes the drying out of the mucous membranes located in the patient's respiratory track. Thus, humidification lessens the chance of injury to delicate tissues and reduces the possibility of an obstruction in a patient's breathing passage as a consequence of insufficient mucous flow.
The medical industry produces two basic types of humidifiers. A first type of humidifier increases the relative humidity of a ventilator circuit in relationship to temperature and produces particulate water droplets or water vapor. A second type of humidifier increases the relative humidity of a ventilator circuit and attempts to produce only molecular humidity. A humidifier that produces molecular humidity without particulate water droplets is preferred to reduce nosocomial infections attributed to humidifiers that produce particulate water droplets such as nosocomial pneumonia. The second type of humidifier is currently implemented in the medical industry with a cascade humidifier which sends gas bubbles through water to produce molecular humidity, but also introduces particulate water droplets or water vapor in the humidified gas.
The Bartels et al U.S. Pat. No. 4,621,632 discloses a humidifier system which utilizes a heater assembly and microprocessor-based control circuitry. The humidifier chamber includes a continuous spiral heat exchange path which extends between a vapor storage chamber and an outlet of a humidifier chamber at which an air heating tube is connected, so that the outgoing air can be delivered to the patient. The microprocessor control circuitry includes a pair of sensors which are responsive to the temperature of the outgoing humidified air at the humidifier chamber outlet and at the patent end of the heating tube. The temperatures sensed are used to control the energization of both the heater assembly and a heating element of a heating tubes to provide air to the patient at a predetermined temperature with minimal rainout.
The Bowles et al U.S. Pat. No. 4,621,633 discloses a portable heated oxygen system for use with hypothermia victims. The heated oxygen system includes a humidifier that is regulated to control the humidified gas outflow between 1 to 20 liters/minute. The system also includes electrical control circuitry for operating heaters for controlling warming of oxygen supplies for inhalation rewarming.
The Douglas et al U.S. Pat. No. 5,006,109 discloses a system for administering gas to a patient during endoscopic or medical procedures that regulates the temperature, pressure, and volumetric flow rate of the gas. The system comprises a temperature sensor, a pressure indicator, and volume flow meter which allows the physician continuous monitoring of the quantitative status of each of these physiological parameters. The system is capable of controlling the temperature, the pressure, and volumetric flow rate of the gas. The system includes an optional humidification system.